Metagenomic and metabolomic dissection of Bacillus albus JZ264-mediated rhizosphere remodeling and growth promotion in pepper (Capsicum annuum L.) under reduced fertilization

Against the backdrop of challenges in balancing plant productivity and ecological conservation under reduced fertilization, this study aimed to identify highly efficient and environmentally adaptable plant growth-promoting rhizobacteria (PGPR) to synergistically balance ecological benefits and pepper cultivation performance under nutrient deficit conditions, while deciphering their underlying mechanisms. Results from in vitro screening, seedling-stage trials, and field inoculation experiments revealed that three strains-Bacillus tequilensis JZ31, Bacillus pumilus JZ38, and Bacillus albus JZ264-possessing IAA-secreting and nutrient-solubilizing capabilities promoted pepper seedling growth via improved photosynthesis and root development when inoculated individually or in combination. Notably, under a long-term 30% reduced fertilization regime, sole inoculation with JZ38 or JZ264 significantly enhanced plant nutrient accumulation, biomass, yield, and fruit quality, with JZ264 demonstrating the most pronounced effects. Metagenomic and metabolomic analyses revealed that while reduced fertilization selectively increased the abundance of nitrogen metabolism-related microbes and activated distinct phosphorus and sulfur metabolic processes via rhizosphere microbial chemotaxis, it concurrently suppressed carbon and nitrogen metabolic pathways and related enzyme activities, thereby reducing available nutrient contents in the rhizosphere. Under reduced fertilization, the inoculated B. albus JZ264 strain broadened the growth-promoting capacity of rhizosphere microorganisms and optimized the rhizosphere microenvironment by selectively recruiting microbes to broadly activate pathways and metabolites associated with nutrient cycling (carbon, nitrogen, phosphorus, sulfur), environmental remediation, and hormone-signal-mediated plant growth promotion. These findings provide valuable biological resources for sustainable agriculture and critical insights into the regulatory mechanisms by which B. albus JZ264 modulates rhizosphere microenvironments and promotes plant growth under fertilizer reduction